I have one and got it after my Lee priming tool wore out. It is slow to load the primers into the little tube. I haven't found a good way to hold the case while priming to prevent getting whacked if a primer does fire inadvertently. You have to make sure you don't cover the case mouth with part of a hand or finger.
I bought it believing that maybe it would have a good, positive "you can stop pushing the primer is as far as it will go" feel to it. Unfortunately it really kinda doesn't. Because of the way you load the tubes with primers I haven't mounted it solid to my bench...I have to move it around too much. If you get a jam or miss feed and it is screwed down you cant just pick it up to clear it so it stops gravity feeding primers.
I think I maybe would have been happier if I had waited for the guy to call me back that makes the stainless steel version of the Lee...
My main concern was positive, absolute, dead end seating of the primer with no mush or wondering if they are all the same depth. Lee makes a little one-at-a-time priming tool that goes on a press called the "Ram Prime"...other than the one at a time slowness it accomplishes everything else I needed and has a good feel.
I have this tool, and there are some aspects of your post that indicate that at least part of your problems are due to operator error or lack of information.
1) The primers aren't slow to load at all, as long as you use the companion primer flipper tray, also made by Forster.
In fact, it has to be about the quickest, easiest system to load a priming tool of any sort that I have seen.
2) I have no problem at all keeping my hand away from the front of the case mouth out of concern for the (highly unlikely, as long as you don't slam the seating lever down) possibility of a primer detonation.
I simply grasp the case on each side just forward of either the base or on either side of the case mouth.
This also brings up that, once the case is properly secured by the shell holder jaws, you need to take your hand away altogether to allow the case to slightly self-align for the primer to seat properly.
3) As long as the shell holders are properly set and snugged down, and as long as the case is properly positioned, there most definitely is a positive stop when seating.
In fact, it's impossible to mess it up, and it's the major selling point of this particular tool.
4) The only time that it should be necessary to move the tool around is when making the adjustments to get the shell holders set just right for your case, explained perfectly above by poster ericbc7.
Also, you don't have to move the tool around to insert the primer tubes, as you first fill the tube, then use a paperclip in the hole at the end that goes into the priming tool to keep the primers from sliding, insert the tube properly, then carefully take out the paperclip to allow gravity to get the primers to drop into the feeding position.
As for having to move it for the adjustment, I take care of that issue by using the excellent Inline Fabrication quick change base/plate system to make it as simple as unscrewing the two securing wingnuts and taking it off of the mounting base, making the adjustments, then putting it back onto the quick change base.